the latter form being the more common one and the one presented by AD.
The expressions for \(f_1\)  and \(f_2\)  can be found in the original paper.[1]} Note that \(\theta \)  cancels in the first expression, and is replaced by the logarithmic frequency moment, which AD found to be the most useful moment for the prefactor of T\(_c\) .
Note that due to the \(f_1\)  and \(f_2\)  factors, T\(_c^{AD}\)  is not exponential in \(\lambda \)  except
where \(\lambda \)  begins to approach \(\mu ^*\)  (very weak coupling) where it is highly sensitive to each quantity, nor is it a meaningful fit to any data.
For the high T\(_c\)  compressed hydrides discussed in Sec. V, each prefactor can approach a 10-20% enhancement of T\(_c\)  (or increasingly more as \(\lambda \)  is increased still further).
